Bash Commands Tutorial

Before we begin, we must clear two concepts: directory and path, to understand Bash commands better.

What is a Directory?

A directory is a folder in any operating system. We use directories to store files and other directories.

What is a Path?

A path specifies the location of a directory or a file. For example:

/home/poridhi/Desktop

It means that to find the Desktop directory, we have to go through home, then poridhi, and finally we will find Desktop.

Types of Paths

  1. Absolute Path: Starts from the root directory of the Linux filesystem. The command pwd (print working directory) prints the absolute path of a directory.

    poridhi@ubuntu:~$ pwd
/home/poridhi

  2. Relative Path: The location of a directory or a file relative to the current working directory. Example:

    poridhi@ubuntu:~/bash$ ls
Image
poridhi@ubuntu:~/bash$ cd Image
poridhi@ubuntu:~/bash/Image$ pwd
/home/poridhi/bash/Image

Fundamental Commands in Bash

1. cd (Change Directory)

Used to change the current working directory.

Examples:

poridhi@ubuntu:~$ cd /home/poridhi/Desktop
poridhi@ubuntu:~/Desktop$

poridhi@ubuntu:~/Desktop$ cd ..
poridhi@ubuntu:/home/poridhi$

poridhi@ubuntu:/home/poridhi$ cd ~
poridhi@ubuntu:~$

poridhi@ubuntu:~$ cd /tmp
poridhi@ubuntu:/tmp$

2. ls (List Directory Contents)

Lists the contents (files and folders) of a directory.

Examples:

poridhi@ubuntu:~$ ls
Desktop  Documents  Downloads

poridhi@ubuntu:~$ ls -a
.  ..  .bashrc  Desktop  Documents

poridhi@ubuntu:~$ ls -al

drwxr-xr-x 2 poridhi poridhi 4096 Jan  1 10:00 Desktop
-rw-r--r-- 1 poridhi poridhi  220 Jan  1 10:00 .bashrc

3. mkdir (Make Directory)

Creates a new directory.

Examples:

poridhi@ubuntu:~$ mkdir new_folder
poridhi@ubuntu:~$ ls
new_folder

4. rmdir (Remove Directory)

Removes an empty directory.

Examples:

poridhi@ubuntu:~$ ls
new_folder
poridhi@ubuntu:~$ rmdir new_folder
poridhi@ubuntu:~$ ls

5. rm (Remove)

Used to delete files or directories.

Examples:

# Remove a file
poridhi@ubuntu:~/Desktop$ rm file.txt

# Remove a directory and its contents
poridhi@ubuntu:~/Desktop$ rm -r old_folder

# Prompt before deleting
poridhi@ubuntu:~/Desktop$ rm -i file.txt

6. touch

Creates an empty file.

Examples:

poridhi@ubuntu:~/Desktop$ touch new_file.txt
poridhi@ubuntu:~/Desktop$ ls
new_file.txt

# Create multiple files
poridhi@ubuntu:~/Desktop$ touch file1.txt file2.txt
poridhi@ubuntu:~/Desktop$ ls
file1.txt  file2.txt

7. cp (Copy)

Copies files or directories.

Examples:

# Copy a file
poridhi@ubuntu:~/Desktop$ cp file1.txt /home/poridhi/Documents/

# Copy a directory
poridhi@ubuntu:~/Desktop$ cp -r folder1 /home/poridhi/Documents/

# Copy and preserve attributes
poridhi@ubuntu:~/Desktop$ cp -p file1.txt /home/poridhi/Documents/

8. mv (Move)

Moves or renames files and directories.

Examples:

# Move a file
poridhi@ubuntu:~/Desktop$ mv file1.txt /home/poridhi/Documents/

# Rename a file
poridhi@ubuntu:~/Desktop$ mv file1.txt file2.txt

# Move multiple files
poridhi@ubuntu:~/Desktop$ mv file1.txt file2.txt /home/poridhi/Documents/

9. cat (Concatenate)

Displays or combines files.

Examples:

# View a file
poridhi@ubuntu:~/Desktop$ cat file1.txt
these are the contents of file1.txt
# Combine files (> overwrite the content of combined.txt)
poridhi@ubuntu:~/Desktop$ cat file1.txt file2.txt > combined.txt
poridhi@ubuntu:~/Desktop$ cat combined.txt
these are the contents of file1.txt
and these are of file2.txt combined in combined.txt
# Append a file (>> appended so combined.txt's contents will stay)
poridhi@ubuntu:~/Desktop$ cat file1.txt >> combined.txt
poridhi@ubuntu:~/Desktop$ cat combined.txt
these are the contents of combined.txt then
contents of file1.txt added after combined.txt contents

10. find

Searches for files or directories.

Examples:

# Find all .txt files in the current directory
poridhi@ubuntu:~/Desktop$ find . -name "*.txt"
./dir1/file2.txt
./dir1/file1.txt
./dir1/file3.txt
./dir1/file4.txt
./file3.txt
./file4.txt

# Find a specific file
poridhi@ubuntu:~/Desktop$ find /home/poridhi -name "file1.txt"
./dir1/file1.txt
# Find by size, larger than 10MB
poridhi@ubuntu:~/Desktop$ find / -size +10M
/boot/vmlinuz-6.8.0-51-generic
/boot/initrd.img-6.8.0-50-generic
/boot/vmlinuz-6.8.0-50-generic
/boot/initrd.img-6.8.0-51-generic

# Exclude certain directories
poridhi@ubuntu:~/Desktop$ find . -name "*.log" -not -path "./backup/*"

11. grep

Searches for patterns in files.

Examples:

cat hello.txt
hello world
this is a word
this is a text to make grep simple
everything is simple
say hello to everyone
# Case-sensitive search
poridhi@ubuntu:~/Desktop$ grep "hel" hello.txt
hello world
say hello to everyone
poridhi@ubuntu:~/Desktop$ grep "every" hello.txt
everything is simple
say hello to everyone
# Case-insensitive search with line numbers
poridhi@ubuntu:~/Desktop$ grep -ni "GRe" hello.txt
2. this is a text to make grep example
# Search in multiple files
poridhi@ubuntu:~/Desktop$ grep "error" *.txt
# Search for a whole word only
poridhi@ubuntu:~/Desktop$ grep -w "every" hello.txt

poridhi@ubuntu:~/Desktop$ grep -w "everyone" hello.txt
say hello to everyone

12. head

Displays the first few lines of a file.

Examples:

# Default first 10 lines
poridhi@ubuntu:~/Desktop$ head hello.txt
hello world
say hello to everyone
.
.
.
# Custom number of lines, first 2 lines
poridhi@ubuntu:~/Desktop$ head -n 2 hello.txt
hello world
say hello to everyone

13. tail

Displays the last few lines of a file.

Examples:

# Default last 10 lines
poridhi@ubuntu:~/Desktop$ tail hello.txt
.
.
.
everything is simple
say hello to everyone
# Custom number of lines, 2 lines
poridhi@ubuntu:~/Desktop$ tail -n 2 hello.txt
everything is simple
say hello to everyone

14. chmod

Changes file or directory permissions.

Examples:

# Add execute permission for everyone
poridhi@ubuntu:~/Desktop$ chmod +x script.sh

# Change to full permissions for owner, group, and others
poridhi@ubuntu:~/Desktop$ chmod 777 file.txt

# Remove write permission for others
poridhi@ubuntu:~/Desktop$ chmod o-w file.txt

15. chown

Changes file or directory ownership.

Examples:

# Change ownership
poridhi@ubuntu:~/Desktop$ sudo chown user1:user1 file.txt

# Change ownership of a directory recursively
poridhi@ubuntu:~/Desktop$ sudo chown -R user1:user1 folder_name

16. df (Disk Free)

Shows disk space usage of file systems.

Examples:

# Show disk space usage in human-readable format
poridhi@ubuntu:~$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       50G   20G   30G  40% /

# Show disk space usage for a specific directory
poridhi@ubuntu:~$ df -h /home/poridhi

17. du (Disk Usage)

Shows disk usage of files and directories.

Examples:

# Show disk usage of a directory
poridhi@ubuntu:~$ du -sh /home/poridhi
1.5G    /home/poridhi

# Show disk usage of all files and directories
poridhi@ubuntu:~$ du -h --max-depth=1

18. free

Displays memory usage.

Examples:

# Show memory usage in human-readable format
poridhi@ubuntu:~$ free -h
              total        used        free      shared  buff/cache   available
Mem:           8.0G        2.5G        4.0G        200M        1.5G        5.2G
Swap:          2.0G          0B        2.0G